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["Galatyuk, Tetyana Prof. Dr." <T.Galatyuk AT gsi.de>]

Dear dilepton team,

while the paper has been now pushed to GPC and in the very advanced stage, i would still like to address several points which we discussed in the early stage of the analysis, but which were not considered to the end. I feel these points must be addressed (prior receiving questions from journal referees and colleagues from the dilepton community). 

Major points:

One of the paper's main messages relies on the interpretation of the fit parameters extracted from the LMR. The choice of fit function is unfortunately poorly explained and needs better motivation in the main text and systematic checks in the methods supplementary material or the analysis note. At the moment this is completely missing.

Generally, a model-independent extraction of the temperature from the invariant mass spectrum is only possible if the electromagnetic spectral function divided by M^2 is approximately constant. This is in general always true in the IMR, in the LMR however this is not true.

At HADES energies due to the very high baryon densities reached in those collisions, the rho meson peak dissolves nearly completely. And only because of this strong melting, it is justified to fit the LMR to extract a temperature. In model calculations, it has been checked that indeed the in-medium spectral function divided by M^2 is nearly constant for the temperature and baryon density range relevant to HADES collisions.

In many places in the main text, it is recognized that the rho meson undergoes significant broadening due to medium effects. So it is completely unclear why one would fit the LMR with a combination of the vacuum rho and an exponential function. The extracted inverse slope parameter is not necessarily a temperature. The remaining rho "peak" makes the slope shallower and leads to an artificially higher extracted inverse slope parameter.

In light of this, the statement that most rho mesons from the hadronic phase are emitted right at the phase boundary doesn't seem to hold up. As the fireball expands the volume gets much bigger. An expected lower yield at lower temperatures gets compensated by the increased volume. In other words, a large range of temperatures makes a significant contribution to the LMR.

Right around the phase boundary due to quark-hadron duality, the emission rates from the QGP and in-medium rho are nearly identical, so the natural explanation of the visible rho peak in the STAR excess spectra is that the late stage of the evolution at temperatures much lower than Tc when the melting of the rho gets less and less is a significant contributor to the LMR.

The chosen fit function of vacuum rho times exponential seems to give unreasonably large values for the inverse slope.

If you want to show that your interpretation is correct then there need to be many more systematic checks. 

Maybe this checks have been done, but there are not documented anywhere.

line30: Fig.1: depicts on x axis Baryon density, text says baryon chemical potential. Note, phase diagram looks different for T-rho or T-muB. Why the red area is increasing towards muB=0? We know it is other way around because errors on Lattice get larger for finite muB. Neutron Stars should be of the same text size as Early Universe. Nuclear liquid-gas phase transition and critical point are missing, neutron star-merger missing. crossover --> chiral crossover. Hadron gas --> Hadron matter and text style as for QGP. Color

Superconductor --> text style as for QGP. 

Insert is true ONLY for RHIC and LHC energy. Arrow y axis is missing. Mee should be of the same style as dN/dM 

Fig 3. includes NOT the final spectra from NA60. We understand very well why final data were possible to publish in proceedings. As before, and i provided txt files with data points, i strongly suggest to use the data from proceedings. The proceedings have quite some citations and have been used e.g. in theory papers.

line 144/145: not clear if we can draw this conclusion. The LMR is a complex interplay between temperature and expanding volume. If the statement in the paper is true would it not mean that all three collision systems were following the same trajectory in the phase diagram? Do SHM results not suggest that this is not true?

line167: well, i thought we agree that we use NA60 point published and only discuss in the text that one could extract different value when fitting different range, taking errors in to account ect. I do not understand why to insist on 245+-17 MeV and create unnecessary discussions in the dilepton community?

Comments to the text:

line5: and in the core of neutron stars --> , in the core of neutron stars and their merger events.

line8: baryon chemical potential --> quark chemical potential

line12: radiated from QGP are ideal probes of the true temperature of  the emitting source, since they do not suffer neither from strong final state interactions nor from  blue-shift effects through the collective motion of the rapidly expanding system

line 13: this is not fully correct, e+e- momentum spectra suffer the same blue-shift effects as other particles, only the 4pi-integrated invariant mass spectrum is blue-shift free

line 16/18: the terms "low" and "intermediate" mass are unclear at this point to an unfamiliar reader

line15: e+e- pairs --> e+e-

line18 low-mass pairs --> low invariant mass pairs

line22: transition temperature --> crossover temperature

line 31:  one should add that the values extracted from the SHM are at freeze-out as muB is different during the fireball evolution as depicted in Fig. 1

line33: e+e− pairs, --> e+e−,

line 62-64: unclear what is meant by this sentence. Rephrase.

line 71: why leave out SIS18 data from this sentence where the melting is even stronger than at SPS and RHIC?

line 95: remove "near the phase transition"

line 97: remove "thermal"

line135: thermal dielectrons

line 136: the charge multiplicity --> the charge track multiplicity

line138: low-mass region (LMR) ->  please define with values what is low-mass region!

line141: while those at IMR -> please define with values the IMR region!

This is very essential information. For those who do not need it will skip it, bt experts in the field need these values!

line 148: "in-medium resonance structure" .... but what is used is the vacuum BW shape of the rho

line 163: remove "slightly"

line 175:  if the IMR temperature is contaminated, should it be called "apparent" temperature?

Fig4. and Fig1 are somehow inconsistent with each other. In Fig. 1 the initial muB is different from the muB at freeze-out from the SHM but in Fig4 both points from early time temperature and late time temperature are placed at the same freeze-out muB

line182: Tc --> Tpc  this is so called pseudo-critical T

line 187: This fit is not justified ... if the rho is not melted you can not fit with the M^(3/2) exp(-M/T) function and call the inverse slope parameter a temperature. The fact that you get similar fit parameters for all energies and both ways of fitting (this one and vacuum BW * exp) shows the methods currently used in the analysis are giving arbitrary results.

line 201: the temperature could not be higher, but it would be lower if the remaining rho peak is taken into account properly, or?

line 211: no constant temperature. In each space-time evolution model (hydrodynamic, adiabatic fireball, coarse-grained transport) the temperature drops while the volume increases 

methods chapter line 126/127: if the error bars on the experimental data are taken seriously then both models describe the data.

Thanks for considering and we are happy to discuss.

Many greetings,

Tetyana and TU team

---

From: Star-dilepton-l <star-dilepton-l-bounces AT lists.bnl.gov> on behalf of Frank Geurts <geurts AT rice.edu>
Sent: Tuesday, June 27, 2023 3:34:20 PM
To: Brandenburg, Daniel
Cc: Star-dilepton-l AT lists.bnl.gov
Subject: Re: [Star-dilepton-l] Dilepton meeting reminder

 

Hi,

I won’t be able to attend as the STAR Analysis Workshop is ongoing this week. I encourage people to attend and take the opportunity to learn about the many ongoing (BES) analyses. At 10h30 we will have the PWG summaries.

-Frank



> On Jun 27, 2023, at 8:27 AM, Brandenburg, Daniel <brandenburg.89 AT osu.edu> wrote:
>
> Hi all,
>  This is a reminder for our dilepton meeting.  Please upload any slides you plan to present. DRUPAL:
> https://drupal.star.bnl.gov/STAR/event/2023/06/27/Dielectron-Focus-Group-Meeting
>  ZOOM:
> https://osu.zoom.us/j/95443162992?pwd=UEdHYXlqdk52c1NObXpXc044ZXJ4QT09
>  Talk to you soon.
>  Daniel Brandenburg
> Assistant Professor
> College of Arts and Sciences
> Department of Physics
> Ohio State University
>   _______________________________________________
> Star-dilepton-l mailing list
> Star-dilepton-l AT lists.bnl.gov
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